1. Field of the Invention
The present invention relates to demulsification and more particularly to the use of polyvalent metal cations in combination with polydithiocarbamic acid compositions and certain hydrotropes as broad spectrum demulsifiers.
2. Description of Prior Art
Many disparate types of emulsions are encountered in a number of different industries. An emulsion is a mixture of two immiscible liquids, one being dispersed in the form of small droplets through the other. Oil-and-water emulsions are found in the form of water-in-oil emulsions or oil-in-water emulsions, the latter form being referred to sometimes as reverse emulsions. Emulsions are stabilized by the presence of surfactants and solids in the interfacial area and by the presence of a charge such as when water is the continuous phase. In addition, many other factors can affect emulsion stability. Among these factors may be noted pH, viscosity, particle size, density disparities, phase composition, mechanical shears and so forth.
As a result of this large number of factors affecting emulsion stability, emulsions differ widely in character and involve complicated interactions of factors, making the predictability of the efficacy of a particular demulsifier on a particular type of emulsion nearly impossible without a test. Thus, the distinctive characteristics of emulsions and the myriad of differences among emulsions have required a wide variety of demulsifier types for use with the wide variety of emulsions in existence.
One type of demulsifier that has been discovered with particular applicability to reverse emulsions is that of U.S. Pat. Nos. 4,689,177, 4,826,625, and 5,089,619 which are incorporated herein by reference. Typically, each type of demulsifier is effective for only a particular type or small range of types of emulsions. In fact, for example, it is common for a demulsifier that is found to be effective in resolving an emulsion that occurs in connate water at one oil well to be found to be ineffective even on what otherwise would be expected to be the same type of emulsion at a nearby well, even in the same production field. Therefore, hundreds or thousands of different demulsifiers have been developed to treat the various emulsions that are encountered.
This particularity of demulsifiers to specific emulsions creates many serious problems. Many different demulsifiers must be synthesized by many different processes and a large number of demulsifiers must be stocked, with adequate supplies of each demulsifier. In many cases, sufficiently effective or low cost demulsifiers have yet to be found. In addition, the various demulsifier types are based on many different types of unrelated chemistries and theories of operation, defying on ability to apply a single unified theory of demulsification and demulsifier selection. Thus, the process of locating a satisfactory demulsifier for a particular emulsion often involves a lengthy series of trials and errors, wrong paths and frequent dead ends. As a result, a testing process, which is often extensive and time-consuming, must be carried out for each type of emulsion in order to locate an effective demulsifier, and if the emulsion changes somewhat, a new demulsifier might have to be located. And it is not uncommon that even after such arduous searches, no satisfactory demulsifier is located. In the meantime, production is lost and shut-downs may result. Further, without a satisfactory demulsifier, increasing environmental concerns and the need to meet increasingly stringent governmental regulations might require the permanent shutting down of some wells and production fields.
Accordingly, many industries have been searching futilely for decades for a convenient demulsifier that is effective over a broad spectrum of emulsions. It is desired that such demulsification be relatively simple and economical in that it requires the simple addition of a composition as opposed to the use of mechanical demulsification techniques. Moreover, it is believed that the optimal composition be a blend that permits adaption and optimization for a wide variety of emulsions by simple adjustment of the blend components and their relative proportions. In particular, a series of demulsifiers based on a single chemistry and theory is desired so that a demulsifier may be tailored for a particular emulsion without the need for such extensive testing and often futile procedures that are so prone to wrong tracks.